Early sensitivity for eyes within faces: A new neuronal account of holistic and featural processing

Abstract

Eyes are central to face processing however their role in early face encoding as reflected by the N170 ERP component is unclear. Using eye tracking to enforce fixation on specific facial features, we found that the N170 was larger for fixation on the eyes compared to fixation on the forehead, nasion, nose or mouth, which all yielded similar amplitudes. This eye sensitivity was seen in both upright and inverted faces and was lost in eyeless faces, demonstrating it was due to the presence of eyes at fovea. Upright eyeless faces elicited largest N170 at nose fixation. Importantly, the N170 face inversion effect (FIE) was strongly attenuated in eyeless faces when fixation was on the eyes but was less attenuated for nose fixation and was normal when fixation was on the mouth. These results suggest the impact of eye removal on the N170 FIE is a function of the angular distance between the fixated feature and the eye location. We propose the Lateral Inhibition, Face Template and Eye Detector based (LIFTED) model which accounts for all the present N170 results including the FIE and its interaction with eye removal. Although eyes elicit the largest N170 response, reflecting the activity of an eye detector, the processing of upright faces is holistic and entails an inhibitory mechanism from neurons coding parafoveal information onto neurons coding foveal information. The LIFTED model provides a neuronal account of holistic and featural processing involved in upright and inverted faces and offers precise predictions for further testing.

Neural processing of fearful and happy facial expressions during emotion-relevant and emotion-irrelevant tasks: A fixation-to-feature approach

“…This fixation effect reflects hemifield presentation effects as most of the facial information was in the left visual field when fixation was on the right eye and the right visual field when fixation was on the left eye (Fig.1A). This effect mirrors fixation effects reported by recent studies using similar gaze-contingent procedures (de Lissa et al, 2014;Neath & Itier, 2015;Nemrodov et al, 2014;Zerouali, Lena, & Jemel, 2013).…”

“…3A) compared to the nose and mouth fixations (de Lissa et al, 2014;Neath & Itier, 2015;Nemrodov et al, 2014). This larger amplitude for the eyes was also found with the mean amplitude analysis at lateral-posterior sites between 150-200ms and supports the idea of a special role for the processing of eyes at the level of the face structural encoding.…”

“…A face stimulus was then presented offset so as to put the desired feature in fovea, at the location of the fixation cross. We expected to replicate the findings of Neath and Itier (2015) regarding low-level stimulus position effects on the P1, as well as the larger N170 amplitude for fixation to the eyes compared to the nose and mouth (see also de Lissa et al, 2014;Nemrodov, Anderson, Preston, & Itier, 2014). We also hoped to reproduce their distinct spatio-temporal pattern of fear and happiness effects.…”

“…1, P1 and N170 components were sensitive to fixation location. Fixation effects on the P1 reflected differences in face position on the screen (Fig.1A) whereas effects on the N170 reflected an eye-sensitivity during encoding of the structure of the face (Nemrodov et al, 2014), as discussed in section 2.3. We come back to these effects in the general discussion.…”

“…Given the more lateral position of the face for the eye fixation locations compared to the midline fixation locations (nose and mouth), we would expect to see smaller, rather than larger, N170 amplitude for fixation to the eyes if this N170 eye sensitivity reflected a mere effect of face position. Nemrodov et al (2014) also showed that the same eye fixation locations did not yield these larger N170 amplitudes when the eyes were not present in fovea (in eyeless faces), despite the same positions of those faces on the screen, thus ruling out a mere effect of face position and demonstrating the dependence of this sensitivity to the presence of eyes in fovea.…”